1. Field of the Invention
The present invention relates generally to the field of magnetohydrodynamic (MHD) machines and, more particularly, is concerned with a MHD turbomachine construction for electric motor and generators.
2. Description of the Prior Art
A homopolar dc motor or generator is inherently a high current, low voltage device. In a typical homopolar machine, the conductor is rotated at as high a speed as practical, utilizing a high current flow, and the magnetic field traversed by the moving conductor is made as large as practical, maximizing the resulting voltage. Although the desire is to transmit power through these machines using a high voltage, nonetheless the resulting output voltage is relatively low.
The output voltage developed is proportional to the following parameters: the magnetic flux field (B); the length (L) of the conductor traversing the magnetic field; and the transverse or tangential velocity (V) of the conductor through the magnetic field. In a typical homopolar machine, there are practical limits on each of the above parameters, B, L and V. In other words, increasing any one of these parameters has practical limitations.
For instance, the capability of increasing the magnitude of magnetic field is ultimately limited by reaching the saturation point of the iron core of the homopolar machine. Increasing the effective length of the conductor, such as by use of multiple, nested armature circuits, disadvantageously increases the weight of and the space occupied by the machine. Further, such circuits presently employ current collection devices at each end of the conductor which easily exhaust space requirements. In the case of solid current collectors, an increase in frictional forces at the contact interface between the brushes and slip rings of the homopolar machine provides practical limits to the ability to increase the tangential velocity of the conductor through the magnetic field. Conventional liquid metal current collectors have similar limits imposed by viscous loss.
In summary, the two major problems in the design of high power density dc machines are the maximization of the length and velocity of a conductor traversing a magnetic field, and the construction of current collection systems to transmit current from rotating to stationary conductors. Finding solutions to these problems is a long-felt need and presents a difficult challenge.